Refrigerator and method of manufacturing the same

ABSTRACT

A refrigerator uses a vacuum heat insulation material. The refrigerator includes a door including a space part having a predetermined volume and a housing having a hole to allow communication between inner and outer sides of the space part. The space part includes, as a core material, an open cell polyurethane foam formed by a foam material injected via the hole to fill the space part.

Pursuant to 35 U.S.C. §119(a), this application claims the benefit of Korean Patent Application No. 10-2013-0057554, filed in Korea on May 22, 2013, which is hereby incorporated by reference as if fully set forth herein.

FIELD

The present disclosure relates to a refrigerator and a method of manufacturing the same, and for example, to a refrigerator including a door with improved insulation performance.

BACKGROUND

In general, refrigerators store food at low temperature and maintain the temperature of a storage compartment at a refrigerating or freezing temperature using a refrigerating or freezing cycle. In this regard, refrigerators are electric products capable of keeping stored foods cool or frozen.

SUMMARY

In one aspect, a refrigerator includes a main body, a storage compartment defined in the main body, and a door configured to selectively open or close the storage compartment. The door includes a housing that defines an external appearance of the door and that has a space part within the housing to define an interior space of the door. The door also includes a hole that allows communication between inner and outer sides of the space part and an open cell polyurethane foam that is filled in the space part by introducing a foam material into the space part through the hole. The space part is vacuum evacuated and sealed in a state in which the space part is filled with the open cell polyurethane foam.

Implementations may include one or more of the following features. For example, the foam material may be injected into the space part through a pipe inserted into the hole and the space part may be evacuated through the pipe. The refrigerator also may include a sealing member configured to seal the hole.

In some implementations, the hole includes an injection hole that enables injection of the foam material and an exhaust hole that enables exhaust of air present in the space part. In these implementations, the injection hole and the exhaust hole may be located at a same position, and the foam material may be injected through the injection hole and, at a same time, air inside the space part may be discharged to an outside thereof via the exhaust hole. Further, in these implementations, the injection hole and the exhaust hole may be arranged at a same surface of the housing.

In addition, the space part may include a getter configured to absorb gas or moisture. Further, the housing may be formed of a metal material, and a boundary portion between adjacent surfaces of the housing is welded.

In some examples, the housing may include a body part having an opening and a cover configured to close the opening of the body part. In these examples, the body part and the cover may be formed of acrylonitrile-butadiene-styrene (ABS) resin. Also, in these examples, the hole may be defined in the body part.

The body part and the cover may be adhered to each other by thermal fusion. Inner circumferential surfaces of the body part and the cover may be plated or deposited with a metal.

In some implementations, the open cell polyurethane foam may be formed by reaction between a polyol composition that includes a polyol and a cell opening agent in combination and a polyisocyanate composition that includes a polyisocyanate compound, where the cell opening agent may be a metal salt of a fatty acid having a hydroxyl group capable of reacting with isocyanate. In these implementations, the cell opening agent of the open cell polyurethane foam may react with an isocyanate group and may chemically combine to a polyurethane chain. Also, in these implementations, the open cell polyurethane foam may have a cell opening rate of 90% or more. Further, in these implementations, the open cell polyurethane foam may have an average cell size of 100 μm or less.

In another aspect, a refrigerator includes a main body and a storage compartment defined in the main body. The refrigerator also includes an outer case that defines an external appearance of the main body and an inner case disposed in the outer case and defining the storage compartment in the main body. The refrigerator further includes a space part disposed between the outer case and the inner case and having a predetermined volume, a hole that is defined in at least one of the outer case or the inner case and that allows communication between inner and outer sides of the space part, and an open cell polyurethane foam that is filled in the space part by introducing a foam material into the space part through the hole. The space part is evacuated and sealed in a state in which the space part is filled with the open cell polyurethane foam.

Implementations may include one or more of the following features. For example, foam material is injected into the space part through a pipe inserted into the hole and the space part is vacuum evacuated through the pipe. Also, the refrigerator may include a sealing member configured to seal the hole.

In some implementations, the hole may include an injection hole that enables injection of the foam material and an exhaust hole that enables exhaust of air present in the space part. In these implementations, the injection hole and the exhaust hole may be located at a same position, and the foam material may be injected via the injection hole and, at a same time, air inside the space part may be discharged to an outside thereof via the exhaust hole.

In yet another aspect, a method of manufacturing a refrigerator includes a door that includes a housing that defines an external appearance of the door and that has a hole that allows communication between inner and outer sides of a space part defined in the housing. The method includes inserting a pipe into the hole, injecting foam material into the space part through the pipe, and forming an open cell polyurethane foam in the space part of the housing by foaming a foaming solution. The method also includes evacuating the space part through the hole to establish a vacuum state within the space part of the housing and, after injecting the foam material into the space part through the pipe, forming the open cell polyurethane foam in the space part of the housing and evacuating the space part through the hole, sealing the hole.

Implementations may include one or more of the following features. For example, the method may include adding, after injecting the foam material into the space part through the pipe, a cell opening agent that enables formation of an open cell. In addition, the method may include inserting a getter before injecting the foam material into the space part through the pipe.

In some implementations, the housing may include an injection hole and an exhaust hole, the injecting may be performed through the injection hole, and the evacuating may be performed through the exhaust hole. In these implementations, injecting the foam material into the space part through the pipe may be performed simultaneously with an exhaust process that removes air inside the space part through the exhaust hole.

In yet another aspect, a method of manufacturing a refrigerator door that includes a space part having a predetermined volume and a housing that defines an external appearance of the door and that has a foaming agent injection hole and a vacuum exhaust hole to allow communication between inner and outer sides of the space part. The method includes filling the space part with an open cell polyurethane foam as a core material by injecting a foaming agent via the foaming agent injection hole. The method also includes sealing the foaming agent injection hole after completing the filling, discharging air inside the space part via the vacuum exhaust hole, and sealing the vacuum exhaust hole after the discharging.

It is to be understood that both the above description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the subject matter claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example refrigerator;

FIG. 2 is a sectional view of an example refrigerator taken along line A-A of FIG. 1;

FIG. 3 is a sectional view of another example refrigerator taken along line A-A of FIG. 1;

FIG. 4 is a perspective view of an example door in which a single hole is formed;

FIG. 5 is a perspective view of the example door into which a pipe is inserted;

FIG. 6 is a sectional view of an example door including an injection hole and an exhaust hole;

FIG. 7 is a sectional view of an example door including a pipe and a sealing member;

FIG. 8 is a sectional view of an example main body and an example cover of the door of FIG. 5, taken along line B-B of FIG. 5;

FIG. 9 is a sectional view of the example door of FIG. 5, an inner circumferential surface of which is plated, taken along line B-B of FIG. 5;

FIG. 10 is a scanning electron microscope (SEM) image of an open cell polyurethane foam;

FIG. 11 is a graph showing a relationship among pressure, cell diameter, and thermal conductivity; and

FIG. 12 is a flowchart illustrating an example refrigerator manufacturing method.

DETAILED DESCRIPTION

FIG. 1 illustrates a structure of an example refrigerator 10. Referring to FIG. 1, the refrigerator 10 includes a main body 20 that defines a storage space that is configured to store foods, doors 30 to open or close a refrigerating compartment 27 and a freezing compartment 28, and a machinery compartment to perform a refrigerant condensation cycle.

The main body 20 includes an inner case 24 (see FIG. 3) that defines a storage space, an outer case 22 (see FIG. 3) to accommodate the inner case 24, and a heat insulation material disposed between the inner case 24 and the outer case 22. Due to the heat insulation material, an impact of external temperature on an internal temperature in the storage space is reduced.

In the refrigerator 10, polyurethane foam, formed through injection of a polyurethane foam solution and foaming of the solution, is filled between the outer case 22 and the inner case 24. Closed cell polyurethane foam may be located between the inner case 24 and the outer case 22 of a refrigerator, but such a structure may have gas inside cells and, thus, may have a thermal conductivity of 0.0160 kcal/mhr° C.

That is, due to inclusion of air inside the closed cell polyurethane foam, the insulation performance may be limited. Refrigerator doors are frequently opened and closed and, thus, may be easily impacted by external temperature. In fact, use of door-in-door refrigerators is increasing and, thus, insulation problems thereof due to frequent opening and closing of doors may occur.

To achieve insulation by inserting a heat insulation material alone into a refrigerator, the thickness of a heat insulation material has to be secured to some extent, which may cause the thickness of the heat insulation material to increase. Thus, the thickness of a wall between an inner case and an outer case may increase and, accordingly, the size of the refrigerator may increase.

When insulation performance is enhanced by forming a vacuum space portion between an outer case and an inner case of a refrigerator, an increase in volume of the refrigerator due to stacking of heat insulation materials may be reduced.

However, the vacuum space portion may have a large sectional area and, thus, insulation performance of a refrigerator may be reduced by even a small increase in pressure due to air permeation and moisture permeation from the outside. The reduction in performance occurs because insulation performance obtained by such a vacuum space portion can be maintained only under high vacuum.

In addition, to maintain an external appearance of a vacuum space portion under high vacuum conditions from external impact or the like, outer and inner cases of refrigerators may involve complicated structures and manufacturing processes.

As illustrated in FIG. 1, the refrigerator includes the main body 20 that defines storage compartments 26 (see FIGS. 2 and 3) and doors 30 rotatably arranged at the main body 20.

The main body 20 includes an outer case 22 (see FIG. 3) that defines an external appearance of the main body 20 and an inner case 24 (see FIG. 3) that is disposed inside the outer case 22 and defines the storage compartments 26 within the main body 20.

The storage compartments 26 of the main body 20 include a refrigerating compartment 27 and a freezing compartment 28. The refrigerating compartment 27 and the freezing compartment 28 may be provided at inner sides thereof with a plurality of drawers and shelves to accommodate various foods.

In addition, the door 30 of the refrigerating compartment 27 or the freezing compartment 28 may be provided at a rear surface thereof with a plurality of baskets to accommodate foods and, as desired, may be provided with an ice maker, a dispenser, a home bar, or the like. In addition, the door 30 may be provided with a door handle 32 that enables a user to open the door 30.

FIG. 2 illustrates an example refrigerator in which a vacuum heat insulation material is applied to doors of the refrigerator. FIG. 3 illustrates the refrigerator of FIG. 2 in which a core material 46 fills the doors thereof and a space between the outer case 22 and the inner case 24 and, thus, serves as a supporting body and a vacuum heat insulation material.

Hereinafter, the door 30 of the refrigerator will be described in more detail with reference to the following drawings.

FIGS. 4 and 5 illustrate an example of the door 30.

The door 30 opens or closes the storage compartment 26 of the main body 20 and includes a space part 49 (see FIG. 6) having a predetermined volume and a housing 34 having a hole 42 to allow communication between inner and outer sides of the space part 49. The space part 49 and the housing 34 define an external appearance of the door 30. A foam material is injected into the space part 49 via the hole 42 and a core material, which is open cell polyurethane foam formed by a foaming solution, fills the space part 49.

An inner surface of the housing 34 contacts the storage compartment 26 and an outer surface of the housing 34 defines the external appearance of the door 30. The housing 34 may be formed of a metal material or acrylonitrile-butadiene-styrene (ABS) resin, but the disclosure is not limited thereto and other materials may be used for the housing 34.

When the housing 34 is formed of steel, the shape of the door 30 is formed by bending the steel and a boundary portion between adjacent surfaces of the housing 34 is sealed by welding. In this case, an increase in pressure of the space part 49 caused by gas generated from the housing 34 may be reduced.

In addition, when the housing 34 is formed by welding steel, sealing may be more effectively performed than when the housing 34 is fixed through engagement of grooves or adhesion of polyurethane.

However, as the number of welds of the housing 34 increases, the risk of welding defects increases. Thus, minimizing the number of welds may improve performance by decreasing the chance of welding defects.

For this operation, as illustrated in FIG. 8, the housing 34 may be formed of ABS resin. In addition, the housing 34 may be designed to include a body part 340 having an opening and a cover 342 to close the opening of the body part 340.

The hole 42 may be arranged at the body part 340. The body part 340 may be closed by the cover 342 through thermal fusion (see 45 of FIG. 9).

When the housing 34 is formed of ABS resin and designed to include the body part 340 and the cover 342, a smaller number of thermal fusion portions 45 may be formed than in a case in which steel is bent and boundary portions thereof are welded, and, thus, a risk of welding defects may decrease. Thus, a housing 34 formed of ABS resin that includes the body part 340 and the cover 342 may be desirable in maintaining a vacuum state.

However, when the housing 34 is made of ABS resin, gas may be generated from the ABS resin. Gases generated from a material of the housing 34 may impact a degree of vacuum formed in the space part 49.

As illustrated in FIG. 9, before thermally fusing (see 45) the cover 342 onto the body part 340 of the housing 34, a process of plating (see 43) an inner circumferential surface of the housing 34 may be performed. Through the plating process, discharge of gas generated from ABS resin to the space part 49 may be reduced (e.g., prevented).

The plating process may be performed by electroplating, chemical plating, hot dipping, evaporation deposition plating, diffusion coating, ion plating, or the like.

In addition, when the housing 34 is made of ABS resin, it may be easier to form a complicated shape of a door liner inside the refrigerator.

FIG. 4 illustrates an example case in which the hole 42 is arranged in the housing 34. FIG. 5 illustrates an example case in which a pipe 44 is inserted into the hole 42. The hole 42 defines a path through which a foam material is injected into the sealed housing 34 and for vacuum evacuation after foaming

In a case in which the pipe 44 is inserted into the hole 42, injection or vacuum evacuation of foam material may be performed. The hole 42 may include one or more holes.

FIG. 6 illustrates an example of the housing 34 in which two holes are formed. The holes may include an injection hole 420 for injection of a foam material and an exhaust hole 422 for forming a predetermined degree of vacuum in the space part 49. Air present in the space part 49 may be discharged via the exhaust hole 422. In some implementations, the foam material for formation of the open cell polyurethane foam is injected via the pipe 44 inserted into the hole 42. Upon injecting the foam material via the injection hole 420, air inside the space part 49 may be discharged to the outside via the exhaust hole 422.

When the foam material is injected, a large amount of gas may be generated. In this regard, the generated gas is discharged to the outside via the exhaust hole 422. Thus, a case in which the core material is unable to densely fill the space part 49 due to gas generated in the foam material injection process or a case in which the foam material reversely flows due to internal pressure when injecting the foam material may be reduced (e.g., prevented) by arranging two holes.

In addition, the injection hole 420 and the exhaust hole 422 may be arranged at the same surface of the housing 34.

When injecting the foaming solution, arrangement of the injection hole 420 and the exhaust hole 422 at the same surface may be desirable in consideration of an air flow path in which air descends due to pushing of the foaming solution, flows towards an exhaust port, and ascends toward the exhaust hole 422. This air flow path may efficiently induce air exhaust.

Instead of separately arranging the injection hole 420 and the exhaust hole 422, the injection hole 420 and the exhaust hole 422 may be formed at the same position. That is, injection of the foam material and air exhaust may be performed using a single hole.

Before injection of the foaming solution, a getter 40 may be inserted. The getter 40 serves to absorb gas or moisture generated inside the space part 49.

FIG. 7 illustrates an example of the housing 34 in which, after completing injection of the foam material via the pipe 44 inserted into the injection hole 420, the pipe 44 is removed and the injection hole 420 is sealed by a sealing member 48.

In a state in which a core material 46 is filled, the space part 49 is vacuum evacuated via the pipe 44 inserted into the exhaust hole 422. Air in the open cell of the core material 46 is also vacuum evacuated and thus the space part 49 may form a predetermined degree of vacuum. Such a vacuum state determines insulation performance of the refrigerator.

When vacuum evacuation via the pipe 44 inserted into the exhaust hole 422 is completed, the pipe 44 is removed and the exhaust hole 422 is sealed and, consequently, the housing 34 defines a completely sealed space.

In addition, the refrigerator may include a space part having a predetermined volume between the outer case 22 and the inner case 24. A hole to allow communication between inner and outer sides of the space part may be arranged at any one of the outer case 22 and the inner case 24.

The space part may be filled with a foam material via the hole, and a core material, which is open cell polyurethane foam formed by a foaming solution, may fill the space part.

In a state in which the core material is filled, the space part is vacuum evacuated via the hole. After vacuum evacuation, the exhaust hole 422 may be sealed by a sealing member 48.

FIG. 10 is a scanning electron microscope (SEM) image of the open cell polyurethane foam.

The space part 49 arranged in the housing 34 is filled with a foam material for forming the open cell polyurethane foam via the hole. After injection of the foaming solution, the open cell polyurethane foam is formed through a foaming process.

To use the open cell polyurethane foam as a core material of a vacuum heat insulation material, the open cell polyurethane foam maintains low thermal conductivity for a long period of time. Such low thermal conductivity largely depends upon the size of cells of the open cell polyurethane foam, and, thus, it may be desirable to minimize cell size to prepare an open cell polyurethane foam for forming a core material of a vacuum heat insulation material.

A second considering factor in using the open cell polyurethane foam as a core material of a vacuum heat insulation material is a cell opening rate. When a small amount of closed cells is present in the open cell polyurethane foam, gas of a foaming agent present in cells may leak towards the core material as time elapses even though initial insulation is excellent. Thus, vacuum pressure of foam of a vacuum heat insulation material may be reduced and, accordingly, insulation performance of the foam may be deteriorated.

The open cell polyurethane foam, which is a core material, may have a relatively small cell size and a very high cell opening rate and may be used as a core material of a vacuum heat insulation material. With this configuration, the open cell polyurethane foam may exhibit efficient insulation performance even in a relatively low degree of vacuum. In addition, the open cell polyurethane foam may be well suited to building structures or impact absorption, or for use as a core material of a vacuum heat insulation material.

To form a core material having excellent cell opening rate and a relatively small cell size, a reactive cell opening composition including a base oil and a metal salt of a fatty acid having a hydroxyl group capable of reacting with an isocyanate group may be added to the foaming solution.

The reactive cell opening composition may be formed as a grease-type mixture composition using a silicon oil surfactant or the like as a base oil and thus may maintain dispersibility at the molecular level. In addition, in a process of forming polyurethane foam to be prepared, a cell opening agent may be chemically combined to a polyurethane main chain by reaction between a hydroxyl group (—OH) of a reactive cell opening agent and isocyanate (—NCO) and, thus, the reactive cell opening composition may perform effective cell opening performance at the molecular level. Accordingly, system instability and non-uniform cell formation according to formulation problems caused when a conventional aqueous cell opening agent is used or disadvantages according to dispersibility and mechanical abrasion during manufacturing processes caused when a solid powder-type cell opening agent is used may be addressed. In addition, cell opening may be effectively performed using a relatively small amount of a cell opening agent.

The base oil is not particularly limited so long as it is capable of satisfactorily dispersing a reactive cell opening agent in the form of a metal salt of a fatty acid. For example, the base oil may be an oil-type surfactant. In some examples, the same surfactant as that used as a component of a polyol composition, which will be described below, may be used. For example, the base oil may be a silicon oil surfactant. Various kinds of silicon oil surfactants may be used and the disclosure is not limited to particular silicon oil surfactants.

The reactive cell opening agent may be a metal salt of a fatty acid having a hydroxyl group capable of reacting with an isocyanate group. A synthesis method of the reactive cell opening agent is not limited and the reactive cell opening agent may be obtained by reaction between a fatty acid having a hydroxyl group and a metal hydroxide. A metal salt may be separately synthesized and then added to the reactive cell opening composition, and neutralization may be induced in the composition by adding a fatty acid and a metal hydroxide to the base oil.

In this regard, the fatty acid may be a saturated or unsaturated fatty acid and may be selected from among C₈-C₃₀ fatty acids. In some implementations, the fatty acid may be a saturated fatty acid. Examples of saturated fatty acids include, but are not limited to, caprylic acid (C8), capric acid (C10), lauric acid (C12), myristic acid (C16), palmitic acid (C16), stearic acid (C18), arachidic acid (C20), behenic acid (C22), and lignoceric acid (C24). The hydroxyl group may be a primary hydroxyl group positioned at the end of a fatty acid. In some examples, the hydroxyl group may be a secondary hydroxyl group positioned at the middle of a hydrocarbon group of a fatty acid, such as 12-hydroxystearic acid (12HSA).

The metal hydroxide may be lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂), and the like, but the disclosure is not limited thereto.

The amount of the reactive cell opening agent, which is a metal salt of a fatty acid, may be 10 wt % to 50 wt % based on 100 parts by weight of the cell opening composition. When the amount of the reactive cell opening agent is less than 10 wt %, to adjust the concentration of the cell opening agent needed for a polyol composition to prepare polyurethane foam, the cell opening composition may be used in a relatively large amount and, thus, an excess of base oil may be added, which causes instability of a foaming system. When the amount of the reactive cell opening agent exceeds 50 wt %, the concentration of the reactive cell opening agent in the cell opening composition may be excessively high and, thus, the viscosity of the composition may increase. Accordingly, it may be difficult to disperse the cell opening agent in the base oil at the molecular level.

In addition, to form the open cell polyurethane foam, a polyol composition including a polyol and a cell opening agent in combination may be used. The cell opening agent may be added, to the polyol composition, as a metal salt of a fatty acid having a hydroxyl group capable of reacting with isocyanate

In this regard, the cell opening agent may be the cell opening agent described above and, thus, a detailed description thereof will be referenced, rather than repeated. The cell opening agent may be directly added to the polyol composition and may be added in the form of the above-described cell opening composition to the polyol composition. In some implementations, the cell opening agent may be added in the form of a cell opening composition, which is suitable for dispersion of the cell opening agent. As described above, the base oil of the cell opening composition may be a polyol composition component, for example, a silicon oil surfactant.

The polyol composition forms polyurethane foam through reaction with a polyisocyanate composition. The polyol composition may use formulations used for formation of conventional polyurethane foams. A polyol composition for preparation of a closed cell hard polyurethane foam optimized for use as a heat insulation material may also be used. In addition, general polyol formulations used to prepare an open cell hard polyurethane foam may also be used. The polyol formulations may include a polyol as a main component and a foam stabilizer, such as a surfactant, a catalyst, a nucleating agent, a foaming agent, a cell opening agent, or the like. In this regard, the surfactant and the cell opening agent may be components of the cell opening composition described above.

As the polyol, the same polyetherpolyols as those used to prepare a general hard polyurethane foam may be used alone or in combination. The amount of the polyol may be 70 wt % to 95 wt % based on 100 parts by weight of the polyol composition. Examples of polyols include, but are not limited to, alkylene glycols (e.g., ethylene glycol, propylene glycol, 1,4-butane diol, 1,6-hexane diol, and the like), glycol ethers (e.g., diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, and the like), glycerin, trimethylolpropane, tertiary amine-containing polyols (e.g., triethanolamine, triisopropanolamine, and adducts of ethylene oxides such as ethylene diamine, toluene diamine, and the like and/or propylene oxides), polyether polyols, and polyester polyols. A suitable polyether polyol may be an alkylene oxide, such as ethylene oxide, propylene oxide, or 1,2-butylene oxide, or a polymer of a mixture of these alkylene oxides. The polyether may be a polymer of a mixture of polypropylene oxide or propylene oxide and a small amount (about 12 wt % or less) of ethylene oxide. These polyethers may be capped with about 30 wt % or less of ethylene oxide. Polyester polyols may also be used. The polyester polyols include reaction products of a polyol, for example, diol and polycarboxylic acid or an anhydride thereof, such as dicarboxylic acid or an anhydride thereof. The polycarboxylic acid or the anhydride thereof may be aliphatic, alicyclic, aromatic and/or heterocyclic and may be substituted with a functional group such as a halogen atom. The polycarboxylic acid may be unsaturated. Examples of polycarboxylic acids include succinic acid, adipic acid, terephthalic acid, isophthalic acid, a trimellitic anhydride, a phthalic anhydride, maleic acid, a maleic anhydride, and fumaric acid. Polyols used to prepare polyester polyols may have an equivalent weight of about 150 or less and include ethylene glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-butane diol, 1,6-hexane diol, 1,8-octane diol, neopentyl glycol, cyclohexane dimethanol, 2-methyl-1,3-propane diol, glycerin, trimethylol propane, 1,2,6-hexane triol, 1,2,4-butane triol, trimethylolethane, pentaerythritol, quinitol, mannitol, sorbitol, methyl glycoside, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, dibutylene glycol, and the like. The polyol may have a hydroxyl value of 350 to 450 mgKOH/g. When the hydroxyl value of the polyol is less than 350 mgKOH/g, a polyurethane product with low hardness due to low crosslinking density during reaction may be formed. When the hydroxyl value of the polyol exceeds 450 mgKOH/g, a polyurethane product easily breakable due to excessively high crosslinking density during reaction may be formed.

As the foam stabilizer, one component or a mixture of two or more components may be used to stabilize formed cells and adjust opening of the cells. For example, the foam stabilizer may be a silicon-based surfactant, for example, the base oil of the reactive cell opening composition described above. The surfactant used as the foam stabilizer may be the same material as that used to prepare a general hard polyurethane foam for high heat insulation, and a mixture of one or more kinds may be used to form a foam having a microporous structure that provides heat insulation performance. For example, the foam stabilizer may be a mixture of B-8462 (manufactured by Gold Schmidt Co.) and Niax L-6900 (manufactured by Momentive Specialty Chemicals). The amount of the foam stabilizer (e.g., base oil) may be 0.5 to 5.0 parts by weight based on 100 parts by weight of the polyol. When the amount of the foam stabilizer is less than 0.5 parts by weight, foam stabilization defects may be caused due to low concentration, or the size and distribution of cells may be non-uniform. When the amount of the foam stabilizer exceeds 5.0 parts by weight, foaming defects according to instability of a foaming system due to excessive formation of an aqueous surfactant may be caused.

The amount of the cell opening agent may be 0.2 to 3.0 parts by weight based on 100 parts by weight of the polyol. When the amount of the cell opening agent is less than 0.2 parts by weight, a cell opening rate may be reduced according to a low concentration of the cell opening agent. When the amount of the cell opening agent exceeds 3.0 parts by weight, the size and size distribution of cells may be non-uniform due to excessive formulation of a solid cell opening agent or mechanical abrasion or the like due to excessive presence of a solid-phase cell opening agent in a foaming system may be caused.

To enhance insulation performance of the foam by decreasing cell size, a nucleating agent may be used. As the nucleating agent, a perfluoroalkane-based compound may be used and the amount thereof may be 1.0 to 5.0 parts by weight based on 100 parts by weight of the polyol.

The polyol composition may further include a foaming agent. A hydrocarbon-based physical foaming agent, generally used as a non-halogen-based environmentally friendly foaming agent, such as cyclopentane may be used and a small amount of water may be added as a chemical foaming agent.

The polyol composition may further include a catalyst, and a general catalyst used to prepare a hard polyurethane foam may be added in a general catalyst amount and these catalysts may be used alone or in combination. For example, the catalyst may be a basic amine, for example, secondary aliphatic amine, imidazole, amidine, alkanolamine, Lewis acid, or a metal-organic compound, in particular a tin-based compound. In addition, as an isocyanurate catalyst, a metal carboxylate, in particular potassium acetate and a solution thereof may be used.

The foam also may include an open cell polyurethane foam formed by reaction between a polyol composition including a polyol and a cell opening agent in combination and a polyisocyanate composition including a polyisocyanate compound, in which the cell opening agent is a metal salt of a fatty acid having a hydroxyl group capable of reacting with isocyanate. The polyol composition has already been described above and, thus, a detailed description thereof will be referenced, rather than repeated.

The open cell polyurethane foam may have a cell size of 100 μm or less that is much smaller than that of conventional open cell polyurethane foam and may have a cell opening rate of 80%, particularly 90%, more particularly 98% or more. Thus, the open cell polyurethane foam is used as a core material of a vacuum heat insulation material and may exhibit efficient heat insulation performance even in a relatively low degree of vacuum and may be well suited to building structures or impact absorption or for use as a core material of a vacuum heat insulation material. These significant effects may be obtained by chemically combining a metal salt of a fatty acid having a hydroxyl group capable of reacting with isocyanate, used as the cell opening agent, to a polyurethane chain.

The polyisocyanate composition includes a polyisocyanate compound. In this regard, the polyisocyanate compound is a compound having two or more isocyanate groups. As the polyisocyanate compound, a compound used to prepare a general hard polyurethane foam may be used. For example, the polyisocyanate compound may be at least one isocyanate selected from the group consisting of diphenyl methane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (H12MDI), and isoporonediisocyanate (IPDI). In addition, as the polyisocyanate compound, a product obtained by chemical reaction of a modified multifunctional isocyanate, e.g., organic diisocyanate and/or polyisocyanate, may be used. For example, the polyisocyanate compound may be selected from among diisocyanate and/or polyisocyanate containing an uretdione group, a carbamate group, an isocyanurate group, a carbodiimide group, an allophanate group and/or a urethane group. The polyisocyanate may have a NCO % of 25% to 35%.

The above-described reactive cell opening composition may maintain dispersibility at the molecular level by being formed as a grease-type mixture composition using a silicon oil surfactant or the like as a base oil and may perform effective cell opening performance at the molecular level by chemically combining a cell opening agent to a polyurethane main chain. Thus, system instability and non-uniform cell formation according to formulation problems caused when a conventional aqueous cell opening agent is used or disadvantages according to dispersibility and mechanical abrasion during manufacturing processes, caused when a solid powder-type cell opening agent is used may be addressed. In addition, cell opening may be effectively performed using a relatively small amount of a cell opening agent.

Hereinafter, the cell opening composition, the core material, and relevant particulars will be described in detail with reference to a preparation example and examples. However, these examples are provided for illustrative purposes only and should not be construed as limiting the scope and spirit of the present disclosure.

PREPARATION EXAMPLE 1 Preparation of Reactive Cell Opening Composition

To a 3 L reaction vessel were added a formulation for preparation of polyurethane foam, 700 g of silicon oil used as a surfactant, and 277.9 g of 12-hydroxystearic acid (12HSA) and the resulting solution was heated to about 100° C. while stirred at 1880 rpm to 3600 rpm. Subsequently, a solution in which 22.1 g of lithium hydroxide (LiOH) was dissolved in 100 ml of distilled water at 70° C. was slowly added thereto over the course of 30 minutes to induce acid-base neutralization reaction. After the reaction was completed, the temperature of the reaction vessel was gradually raised to 200° C. and the reaction product was stirred for 1 hour to completely remove moisture contained in the reaction product. Thereafter, the reaction product was slowly cooled to about 60° C. and post treatment was performed using a roll mill and a filter, thereby preparing a composition having a solid content of 30 wt % and including a grease-type surfactant and a reactive cell opening agent in combination. Table 1 shows a mix ratio represented by wt % of LiOH to the silicon surfactant, and molecular weights and mixed amounts of LiOH and 12HSA.

TABLE 1 Molecular Composition Compound weight (g/mole) Amount ratio LiOH 23.9  22.1 g 30 wt % 12HSA 300 277.9 g Silicon oil — 700.0 g 70 wt %

EXPERIMENTAL EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLE 1 Preparation of Hard Polyurethane Foam

Components shown in Table 2 below were mixed in amounts quantified according to composition ratios shown in Table 2 at room temperature (25° C.) for 4 to 5 seconds using a mechanical mixer with high RPM and the resulting mixture was poured into an open mold having a size of 20x20 cm and a rectangular box shape to induce foam formation. After the reaction was completed, the formed foam was subjected to aging for 24 hours and cut and the size of the cell was measured using a scanning electron microscope (SEM) and is illustrated in Table 2.

In addition, Table 3 below shows measurement results of properties of polyurethane foams prepared according to Experimental Examples 1 and 2 and Comparative Example 1.

TABLE 2 Comparative Experimental Experimental Example 1 Example 1 Example 2 Component Amount (phr) Amount (phr) Amount (phr) A Polyol (OHV 400 420 mmKOH/g) 100 100 100 Catalyst (amine/metal salt) 1.45 1.45 1.45 Foam stabilizer (silicon oil surfactant) 2.2 2.2 2.2 Nucleating agent(perfluoroalkane) 3.0 3.0 3.0 Foaming agent H₂O 2.0 2.0 2.0 Cyclopentane 16.5 16.5 16.5 Cell opening agent 1-Butanol 0 4.0 4.0 Li 12HSA 0 0 2.0 B polyisocyanate (NCO % 31.0-32%) A/B 100/123 100/123 100/123

TABLE 3 Compar- Experi- Experi- ative mental mental Properties Example 1 Example 1 Example 2 Cell opening agent (phr) 1-Butanol 0.0 4.0 4.0 Li 12HSA 0.0 0.0 2.0 Cell size (μm) ~90.0 ~88.0 ~92.0 Cell opening rate (%) 9.7 10.5 98.0 Bulk density (kg/m³) 54.2 54.5 52.2 Condensation intensity (kg/m²) 6.22 6.96 5.48 k-factor (10⁻³ kcal/mhr ° C.) 26.55 26.40 27.13

As shown in Table 3, it can be confirmed that, in Comparative Example 1 in which a cell opening agent was not used, a closed cell hard polyurethane foam having a cell opening rate of less than 10% was formed. In addition, from the result according to Experimental Example 1, it can be confirmed that 1-butanol as a cell opening agent did not properly function as a cell opening agent. However, from the result according to Experimental Example 2, it can be confirmed that, when a reactive cell opening agent is used, an open cell hard polyurethane foam is obtained with excellent properties without damage to cell size and mechanical properties.

That is, it may be difficult to reduce heat insulation performance of the closed cell hard polyurethane foam to a level of heat insulation performance of a foaming gas or less. On the other hand, as described above, when the open cell hard polyurethane foam is used, the foam fills the inside of the housing and thus may support the structure of the refrigerator and maintain a vacuum state over a long period of time. That is, the open cell hard polyurethane foam acts as a supporting body of the inside of the housing and has a cell opening rate of 90% or more and, thus, internal gases leak from cells in a vacuum state, leading to an empty state of the cells.

In general, to enhance heat insulation performance, a vacuum heat insulation material is attached to the inside of a refrigerator. In this case, heat insulation performance corresponds to about 0.0130 kcal/mhr° C. Unlike a conventional refrigerator in which a vacuum heat insulation material is formed and a closed cell polyurethane foam is foamed, when all wall surfaces of a refrigerator are foamed with an open cell polyurethane foam and vacuum evacuated, heat insulation performance may be enhanced to 0.0070 kcal/mhr° C. or less. Thus, when all wall surfaces of the door 30 or the main body 20 are filled with the open cell polyurethane foam through foaming, heat insulation performance may be increased by 50% or more as compared to conventional refrigerators.

FIG. 11 is a graph showing a relationship among pressure, cell diameter, and thermal conductivity.

As illustrated in FIG. 11, in a case in which the same pressure is maintained, thermal conductivity decreases as cell diameter decreases. Thus, the open cell polyurethane foam having a cell diameter of about 100 μm, which is a core material, may maintain low thermal conductivity at a pressure of 1 Pa or less.

Thus, in the refrigerator, the door 30 or the main body 20 is entirely heat-insulated using a vacuum layer and, thus, heat insulation performance of the refrigerator may be increased by 50% or more as compared to conventional refrigerators and air permeation, moisture permeation, and rapid deterioration of heat insulation performance due to increase in pressure by internally generated gases may be reduced (e.g., prevented).

Hereinafter, a method of manufacturing a refrigerator having the above-described structure will be described in detail with reference to FIG. 12.

The space part 49 having a predetermined volume and the housing 34 having a hole to allow communication between inner and outer sides of the space part 49 are arranged, and the pipe 44 is inserted into the injection hole 420 through which a foam material is injected (operation S1). The foam material is injected into the space part 49 via the pipe 44 (operation S2). The getter 40 may be inserted before injection of the foaming solution.

The foam material is foamed to form the core material 46 of an open cell polyurethane foam (operation S3). To form open cells, a reactive cell opening agent may be added. In the injection of the foaming solution, an exhausting process for removal of air in the space part 49 via the exhaust hole 422 may be performed.

After the foaming process is completed, the pipe 44 inserted into the injection hole 420 is removed and the injection hole 420 is sealed (operation S4).

Thereafter, the space part 49 is vacuum evacuated via the pipe 44 inserted into the exhaust hole 422 (operation S5). When a predetermined vacuum state is formed in the space part 49 through the vacuum evacuation process, the pipe 44 inserted into the exhaust hole 422 is removed and the exhaust hole 422 is sealed, thereby forming a completely sealed space (operation S6).

In other examples, first, the core material 46 is prepared so as to have the same shape as that of the door 30 or the main body 20 of the refrigerator and then put into the housing 34 to form the external appearance of the door 30.

The core material 46 is positioned inside the housing 34 and then the housing 34 is sealed. For this operation, the pipe 44 is inserted into the housing 34 to vacuum evacuate the inside of the housing 34 therethrough.

After vacuum evacuation, the pipe 44 is removed and the hole is sealed to form a sealed space. Through these processes, a refrigerator including a door, the inside of which is filled with a vacuum heat insulation material, may be manufactured.

The manufacturing method may also be applied to a space between the outer case 22 and the inner case 24 of the main body 20 of the refrigerator.

In some implementations, the disclosure applies to a refrigerator using a vacuum heat insulation material that maintains a vacuum state and serves to support the structure of the refrigerator and a method of manufacturing the same.

In some examples, the refrigerator may use a vacuum heat insulation material that maintains heat insulation performance and structural stability in spite of external impact or reduction in a predetermined degree of vacuum.

Also, a more efficient material and fabrication shape of a housing for formation of a space to accommodate a vacuum heat insulation material may be provided.

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosure. Thus, it is intended that the present disclosure covers the modifications and variations that come within the scope of the appended claims and their equivalents. 

What is claimed is:
 1. A refrigerator comprising: a main body; a storage compartment defined in the main body; and a door configured to selectively open or close the storage compartment, wherein the door comprises: a housing that defines an external appearance of the door and that has a space part within the housing to define an interior space of the door; a hole that allows communication between inner and outer sides of the space part; and an open cell polyurethane foam that is filled in the space part by introducing a foam material into the space part through the hole, wherein the space part is vacuum evacuated and sealed in a state in which the space part is filled with the open cell polyurethane foam.
 2. The refrigerator according to claim 1, wherein the foam material is injected into the space part through a pipe inserted into the hole and the space part is evacuated through the pipe.
 3. The refrigerator according to claim 1, further comprising a sealing member configured to seal the hole.
 4. The refrigerator according to claim 1, wherein the hole comprises an injection hole that enables injection of the foam material and an exhaust hole that enables exhaust of air present in the space part.
 5. The refrigerator according to claim 4, wherein the injection hole and the exhaust hole are located at a same position, and the foam material is injected through the injection hole and, at a same time, air inside the space part is discharged to an outside thereof via the exhaust hole.
 6. The refrigerator according to claim 4, wherein the injection hole and the exhaust hole are arranged at a same surface of the housing.
 7. The refrigerator according to claim 1, wherein the space part comprises a getter configured to absorb gas or moisture.
 8. The refrigerator according to claim 1, wherein the housing comprises a body part having an opening and a cover configured to close the opening of the body part, wherein the body part and the cover are formed of acrylonitrile-butadiene-styrene (ABS) resin.
 9. The refrigerator according to claim 8, wherein the hole is defined in the body part.
 10. The refrigerator according to claim 8, wherein the body part and the cover are adhered to each other by thermal fusion.
 11. The refrigerator according to claim 8, wherein inner circumferential surfaces of the body part and the cover are plated or deposited with a metal.
 12. The refrigerator according to claim 1, wherein the housing is formed of a metal material, and a boundary portion between adjacent surfaces of the housing is welded.
 13. The refrigerator according to claim 1, wherein the open cell polyurethane foam is formed by reaction between a polyol composition comprising a polyol and a cell opening agent in combination and a polyisocyanate composition comprising a polyisocyanate compound, wherein the cell opening agent is a metal salt of a fatty acid having a hydroxyl group capable of reacting with isocyanate.
 14. The refrigerator according to claim 13, wherein the cell opening agent of the open cell polyurethane foam reacts with an isocyanate group and chemically combines to a polyurethane chain.
 15. The refrigerator according to claim 13, wherein the open cell polyurethane foam has a cell opening rate of 90% or more.
 16. The refrigerator according to claim 13, wherein the open cell polyurethane foam has an average cell size of 100 μm or less.
 17. A refrigerator comprising: a main body; a storage compartment defined in the main body; an outer case that defines an external appearance of the main body; an inner case disposed in the outer case and defining the storage compartment in the main body; a space part disposed between the outer case and the inner case and having a predetermined volume; a hole that is defined in at least one of the outer case or the inner case and that allows communication between inner and outer sides of the space part; and an open cell polyurethane foam that is filled in the space part by introducing a foam material into the space part through the hole, wherein the space part is evacuated and sealed in a state in which the space part is filled with the open cell polyurethane foam.
 18. The refrigerator according to claim 17, wherein foam material is injected into the space part through a pipe inserted into the hole and the space part is vacuum evacuated through the pipe.
 19. The refrigerator according to claim 17, further comprising a sealing member configured to seal the hole.
 20. The refrigerator according to claim 17, wherein the hole comprises an injection hole that enables injection of the foam material and an exhaust hole that enables exhaust of air present in the space part.
 21. The refrigerator according to claim 20, wherein the injection hole and the exhaust hole are located at a same position, and the foam material is injected via the injection hole and, at a same time, air inside the space part is discharged to an outside thereof via the exhaust hole.
 22. A method of manufacturing a refrigerator comprising a door that includes a housing that defines an external appearance of the door and that has a hole that allows communication between inner and outer sides of a space part defined in the housing, the method comprising: inserting a pipe into the hole; injecting foam material into the space part through the pipe; forming an open cell polyurethane foam in the space part of the housing by foaming a foaming solution; evacuating the space part through the hole to establish a vacuum state within the space part of the housing; and after injecting the foam material into the space part through the pipe, forming the open cell polyurethane foam in the space part of the housing, and evacuating the space part through the hole, sealing the hole.
 23. The method according to claim 22, further comprising adding, after injecting the foam material into the space part through the pipe, a cell opening agent that enables formation of an open cell.
 24. The method according to claim 22, further comprising inserting a getter before injecting the foam material into the space part through the pipe.
 25. The method according to claim 22, wherein the housing comprises an injection hole and an exhaust hole, the injecting is performed through the injection hole, and the evacuating is performed through the exhaust hole.
 26. The method according to claim 25, wherein injecting the foam material into the space part through the pipe is performed simultaneously with an exhaust process that removes air inside the space part through the exhaust hole.
 27. A method of manufacturing a refrigerator door comprising a space part having a predetermined volume and a housing that defines an external appearance of the door and that has a foaming agent injection hole and a vacuum exhaust hole to allow communication between inner and outer sides of the space part, the method comprising: filling the space part with an open cell polyurethane foam as a core material by injecting a foaming agent via the foaming agent injection hole; sealing the foaming agent injection hole after completing the filling; discharging air inside the space part via the vacuum exhaust hole; and sealing the vacuum exhaust hole after the discharging. 